Membrane Permeability Flashcards
What molecules can pass freely across the plasma membrane?
Small uncharged polar molecules (water, urea, glycerol)
Hydrophobic molecules and gases (o2, CO2, n2, benzene)
If Gibbs free energy △G is positive the diffusion is _________
Active - change in free energy
If Gibbs free energy △G is negative the diffusion is _________
Passive
What is active transport?
Allows movement of ions/molecules against their concentration or electrical gradient (unfavourable)
Energy required indirectly or directly from ATP hydrolysis
Which cells have high energy expenditure on active transport?
Nerves
Muscle
Erythrocytes
Enterocytes
What are the general intracellular and extracellular Na concentrations?
Outside 145 mM
Inside 12 mM
What are the general intracellular and extracellular K concentrations?
Outside 4 mM
Inside 155 mM
What are the general intracellular and extracellular Cl concentrations?
Outside 123 mM
Inside 4 mM
What are the general intracellular and extracellular Ca concentrations?
Outside 1-2 mM
Inside 100 nM
What is uniport?
Only one type of molecule transported at a time
What is cotransport?
More than one ion/molecules transported at a time
What is symport?
Cotransport in the same direction
E.g. Na/Glucose cotransported in small intestine and kidney
What is antiport?
Cotransport in opposite directions
E.g. NCX.
What is the function of the Na/K ATPase?
Active transporter present in every cell
Transports 3Na out of cell and 2K into cell per ATP molecule hydrolysed
Acts to maintain cellular concentrations of Na and K (form the gradients)
What channels are responsible for resting membrane potential (~-70mV) ?
K diffusion through K+ channels
What is the main function of the K/Na ATPase?
Form sodium and potassium gradients which are necessary for electrical excitability
Also derived secondary active transport (cotransport)
How does the Na/k ATPase regulate ph?
Sodium gradient generated by Na/k ATPase is used to exchange H+ ions out of the cell (1:1 exchange)
What is high intracellular toxic to cells?
Causes precipitation of phosphate (ossification) and Pi can’t be recycled
What is the role of mitochondrial Ca uniporters?
At high cytoplasmic calcium, operate as a buffer to take calcium into mitochondria (facilitated diffusion), induces caspase pathway which induces apoptosis of the cell (cell death at high [Ca2+]
In control of pH which two exchangers are important in lowering acid (H+ leaves)?
- Na/H exchanger (NHX) - one Na in, one H out
- Na dependent Cl-/HCO3- exchanger - one Na in , 1 H out, 1 HCO3 in, 1 Cl out
What does electroneutral mean?
The number of positive/negative charges leaving is equal to the the charge entering
E.g. Na/H exchanger
What is the Na/H exchanger activated and inhibited by ?
Activated by growth factors
Inhibited by amiloride (K+ sparing diuretic)
In control of pH which exchanger is important in lowering base inside cell (HCO3- leaves)?
- Cl/HCO3- anion exchanger - one HCO3- out, 1 Cl in
Important in peripheral circulation
What molecules are important in cell volume regulation?
Water follows osmotically active ions such as Na, K, Cl (6 molecules of water move across membrane per one ion) and organic osmolytes (such as amino acids) into/ out of cell causes shrinking or swelling